The long range objective of this research is to understand the molecular mechanism of insulin resistance in muscle tissue of obese individuals and diabetic patients. The most likely cause of insulin resistance in human muscle is decreased insulin receptor tyrosine kinase activity. The hypothesis is that hyperinsulinemia causes activation of PKC-beta which then serine/threonine phosphorylates and inactivates the insulin receptor to cause insulin resistance in muscles of obese individuals. It was previously demonstrated that: (1) insulin resistance can be induced by incubating insulin sensitive muscle with an activator of PKC. (2) Insulin action and insulin receptor kinase activity are restored in insulin resistant muscles that are treated with a PKC inhibitor. (3) PKC-beta is increased in muscle of obese individuals. (4) Insulin causes membrane associated PKC-beta to be increased in insulin resistant muscles. (5) Overexpression of PKC-beta decreases insulin signaling, and knockout of PKC-beta increases insulin signal transduction, in heart of transgenic mice. This proposal will continue to focus on the insulin receptor and PKC-beta to gain evidence to support the hypothesis. Specific Aim 1: To determine the phosphorylation pattern on the insulin receptor. Specific Aim 2: To investigate the role of hyperinsulinemia in activation of PKC-beta and phosphorylation of insulin receptors. Specific Aim 3: To study insulin action in muscle of PKC-beta knockout mice. Specific Aim 4: To study the serine/threonine phosphatase(s) that reactivates the insulin receptor. It will be possible to study these mechanisms because a large number of obese patients are available for study.